1. Field of the Invention
This invention was supported by grants from the American Dental Association Health Foundation (ADAHF) and The National Institute of Dental Research (NIH).
This invention relates to alloy compounds which undergo stress-induced martensitic transformations at or near mouth or body temperature. A martensitic transformation occurs in these alloys when they transform under stress from a cubic CsCl or B2 type structure, which is stable at elevated temperatures, to a CrB type structure that is stable at a lower temperature. This type of transformation increases the ductility of these alloys. Ductility, as used hereinafter, is defined as the ability of a material to deform plastically without fracturing as measured by elongation or reduction of area in a tensile test. More specifically, the present invention relates to new alloys exhibiting adequate strength for use in dental or medical implants or protheses and enhanced ductility as compared to the known cubic CsCl or B2 type alloys which do not transform. The alloys of the present invention are composed of elements comprising zirconium and/or, optionally, those others in Group IVB of the periodic table, together with selected elements of Groups VIII, IIIA and IVA, most preferably palladium and ruthenium. The adequate strength and enhanced ductility of the new alloys make them suitable for use in the dental or medical areas as for example, castings for crowns, bridges, dental or medical implants or as prosthetic devices.
2. Description of the Prior Art
Methods of enhancing the ductility of high strength steels and other alloys, through a combination of elements enabling the formation of stress-induced martensitic structures appear in the prior art. See for example, Zackay, V.F., Parker, E.R., Fahr, D., and Busch, R., "The Enhancement of Ductility in High Strength Steels", Trans. Asm. 60 252-259 (1967). For examples of zirconium-cobalt-nickel alloys see Lall, C., Loretto, M.H., and Harris, I.R., "Transformation and Deformation Studies of Some Zr(CoNi) Alloys", Acta Met. 26 1631-1641 (1978) and Barraclough, K.G., Hossain, D., and Harris, I.R., "A Study of ZrCo and Related Ternary Phases Represented by the General Formula Zr.sub.50 Co.sub.50-X Ni.sub.x.", 37 Journal of the Less Common Metals 35-57 (1974).
Numerous alloys have been used in the dental and medical areas for firing on dental porcelain, in making porcelain jacketed dental restorations, as cast alloys for removable dental construction, or for use in making surgical implants, see for example, Prasad U.S. Pat. No. 4,576,789, Wagner et al. U.S. Pat. No. 4,551,302, Schaffer U.S. Pat. No. 4,482,323, Nawaz U.S. Pat. No. 4,591,483, Lanam et al. U.S. Pat. No. 4,608,229, Rothaut et al. U.S. Pat. No. 4,576,790 and Steinemann et al. U.S. Pat. No. 4,040,129. The present invention distinguishes itself over the prior art in the number and type of elements composing the alloy and the percent composition of the elements. For example, applicant's alloy contains significantly less palladium than the 60% used by Lanam et al. in the '229 patent. Applicant's alloy further distinguishes itself from Prasad's '789 patent by containing no copper and significantly less palladium than the 70% disclosed in Prasad. Also, applicant's alloy distinguishes itself from the Wagner et al. '302 patent by having no platinum, gold, etc. and significantly less palladium than the 65% suggested therein. The instant alloy further distinguishes itself from Schaffer's '323 patent by containing no silver, tin, etc. and significantly less palladium than the 45% used in Schaffer. Finally, the alloy of the invention distinguishes itself from Steinemann et al. by containing no niobium, tantalum, chromium, molybdenum or aluminum and distinguishes itself from Nawaz and Rothaut et al. by containing no gold.